17th Edition Consumer Units

Following the 2008 changes to the wiring regulations most circuits are now required to be RCD protected and a new type of Consumer unit has become popular for use in domestic properties.

This is commonly called a 17th Edition Consumer Unit. There are various options available to meet the 17th edition that vary from the "just meets the minimum requirements" to "top of the range" units.

What Is Required by the 17th Edition

RCD protection is now required for

1. All sockets up to 20A for general use by ordinary persons (reg 411.3.3) eg general house sockets, garage sockets and cookers with a socket outlet
2. All circuits in a bathroom (reg 701.411.3.3) eg lights, shaverpoint, electric showers
3. All circuits buried in a wall at less than 50mm and without mechanical protection.(reg 522.6.6) eg most cables in a normal home

It is not permitted to have a single 30mA RCD protecting all the circuits and so usually the use of two or more RCDs are required.

Different Setups

The different setups are explained below

Flexible of Fixed Consumer Units

Many of the CUs mentioned below can be bought as either fixed or flexible (sometimes called configurable). A fixed CU does not allow the installer to alter the number of ways served (or not served) by the RCDs.

Dual RCD

This is the basic 17th edition CU. Typical examples are usually fixed 5+5 and 6+6 way split CUs and there is no provision for non RCD positions. These consumer units are best suited to small properties that have no power to external buildings and only a few circuits. It is usual practice to do a mix with the lighting and socket circuits so that in the event of a fault then some lights and some sockets will stay on (eg upstairs lights and downstairs sockets on one RCD with downstairs lights and upstairs sockets on the other RCD) One limitation of this type of CU is that if mains powered smoke alarms are installed then the regs cannot be met if there are socket circuits on both RCDs as smokes should not share an RCD with sockets.

Hi-integrity

A hi-integrity CU is a dual (or more) RCD CU with some non-RCD places. This allows RCBOs to be installed for specific circuits such as smoke alarms or outside power or normal MCBs if the installation allows it. A flexible unit offers the installer more choice over his particular install.

Triple and more RCD

CUs with 3 or more RCDs are now available. Again, they can be fixed or hi-integrity either with or without non RCD spaces. Triple RCD CUs commonly have one of the RCDs with a lower maximum load rating than the other two RCDs.

One RCD with RCBOs

A split load CU with one RCD and a number of non-RCD places. The non RCD places can be used with RCBOs or MCBs (if allowed)

All RCBOs

A CU with all the circuits having individual RCBOs. This is an expensive option but offers the best discrimination in the event of a fault.